1. Field of the Invention
The present invention relates to an integrated circuit with at least one integrated transmission line. The invention further relates to the field of integrated semiconductor circuits (integrated circuit, IC), within the field of transmission lines, integrated into such circuits, for the transmission of high-frequency electrical signals.
2. Description of the Background Art
For the transmission of high-frequency differential signals, symmetrically constructed transmission lines are typically used, which have two straight line branches arranged at a certain distance to one another. The electrical length of such a classic transmission line, which is proportional to the phase shift of the signal to be transmitted, is within the magnitude of the signal wavelength. At a frequency of, e.g., 30 GHz, the free space wavelength is 10 mm, whereas, e.g., at 3 GHz a wavelength of 100 mm results.
The properties, such as, e.g., wave impedance (impedance), propagation constant, or quality (Q-factor), etc., of a classic transmission line can be changed by varying the cross section of the line branches, their distance to one another, their distance to ground, and/or the dielectric constant of the surrounding medium. The geometric length of a classic transmission line, i.e., its dimensions in the signal propagation direction, can be changed by such measures but not critically.
If a transmission line is to be integrated on a semiconductor chip (IC), only a very small area is available for this, whose dimensions are considerably smaller than the geometric lengths, achievable by the aforementioned measures, of classic transmission lines.
To be able to realize longer transmission lengths in an area with predefined dimensions, the lines are typically made meander-shaped, as shown schematically in FIG. 7. It is a disadvantage here that in comparison with a conventional transmission line at the same geometric length of the extended line branches, due to the meander shape, the quality of the transmission line declines and thereby its insertion loss increases. In addition, the geometric line length per unit area can be at best doubled by this approach. Because of the too low values of the electrical length or the phase shift, it is not possible to integrate meander-shaped transmission lines for the transmission of signals in the frequency domain of considerably less than 30 GHz into an IC.